Carbamazepine, a drug useful in the treatment of trigeminal neuralgia and temporal lobe epilepsy, has recently been found to have positive psychotropic effects in patients with manic and depressive illness. The possible effect of carbamazepine on opioid activity in cerebrospinal fluid (CSF) were assessed in patients with affective disorders using a radioreceptor assay that detects total opioid binding activity. No effect of carbamazepine was noted on CSF total opioid activity, although conclusions about its possible effects on discrete opiate systems must await other methodologies. Initial medication-free levels of opioid activity were positively correlated with the degree of antidepressant response to carbamazepine.